Phosphorus-carbon bond formation: new methodologies for hydrophosphinylation reactions

Abstract

The work developed in this dissertation is mostly centered on phosphorus-carbon bond formation and the synthesis of previously inaccessible H-phosphinates. However, the second chapter of this dissertation presents the new methodologies, which were generated to synthesize ester hypophosphites. Even though ester hypophosphites ROP(O)H 2 are essential starting materials for many chemical reactions, no efficient synthesis for their formation has been described in the literature. We now report a novel methodology for the esterification of hypophosphorous acid and its salts, using tetra-, tri- or dialkoxysilanes compounds as starting materials. The produced esters are thermally stable. The reaction mostly produces quantitative yields, tolerates a wide variety of solvents and allows us to generate various esters in 2 hours. To extend the scope of synthesized esters, we developed a modified Stawinski methodology. The reaction produces moderate to good yields of a wide variety of esters. Chapter III describes a new radical P-C bond formation between sodium hypophosphite, triethylborane and alkenes. The reaction conditions are, room temperature, MeOH and a vessel opened to the air. Generation of novel H-phosphinates compounds in excellent yields is achieved. Because of the neutral conditions applied, the reaction tolerates a wide variety of alkenes, when even functionalized alkenes react efficiently. The subsequent chapter is an extension of that radical reaction to alkynes. Generation of original 1,1-bis-H-phosphinic acids has been achieved in moderate to good yields. The compounds are obtained as di-sodium salts and can be subsequently acidified and oxidized to generate known medicinally important bis-phosphonates. The last chapter of this dissertation details the hydrophosphinylation reaction of alkenes and alkynes, catalyzed by palladium. With this new P-C bond formation reaction, a wide variety of catalytic systems can be employed, as well as a broad diversity of hypophosphorous and unsaturated compounds starting materials. The mechanism of the reaction is extremely selective toward hydrophosphinylation, since even aqueous hypophosphorous acid can be utilized without generating any competitive reduction product. In an effort to make the reaction more environmentally friendly, we developed a supported version of the catalytic system Pd 2 dba 3 /xantphos. The catalyst is very efficient, truly recyclable and water tolerant thus making it quite a powerful catalytic system.